Changes in specific gravity (SG) reflecting the water content of the tissue were evaluated during drug-induced epileptiform convulsions and in acute hypertension. Contrary to the expectation of finding lower SG, i.e. increased water content in brain regions showing the blood-brain barrier (BBB) changes due to epileptic seizures or to acute hypertension, these areas revealed an increased SG, i.e. a relatively reduced water content.